In rod-based drilling in the ground, in particular to produce to horizontal borings, a drill head of a drilling rod is driven by a drive device situated on the surface or in a construction pit. The drill rods used consist of individual drill rod lengths connected to each other, which according to the course of the drilling are successively applied to the rear end of the already drilled-in drilling rod and connected thereto.
For rock drilling, i.e. drilling in rock or stone formations, a double drill rod or double rod is used. In these drilling devices the drilling head is additionally driven in a rotating manner via an inner rod of the double drill rod from the drive device arranged on the surface or in the construction pit which also ensures advancing of the drilling head. For this the inner rod is borne in a rotatable manner within an outer rod of the double drill rod. In double drill rods the individual rod lengths both of the outer rod and the inner rod are either screwed to each other or inserted into each other.
To supply electrical consumers in the double drill rod and/or to transmit signals it is necessary to provide electrical connections within the double drill rod. For this it is known to use a conductor or a cable which extends along the inside of the inner drill rod.
A drawback of the existing provision of electrical connections is that the electrical connection for conducing electrical energy—for supplying electrical voltage or power and/or for transmitting data—can only take place in the inner drill rod assembly as it has hitherto been assumed that the conductor or cable has to be protected in the inner drill rod.